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by ptimlin
Wed Jun 12, 2019 3:21 pm
Forum: Automation, sensing and robotics
Topic: Help trying to control 3v relay using GPIO?
Replies: 4
Views: 186

Re: Help trying to control 3v relay using GPIO?

How much current does the relay coil need to operate properly. By my calculation, your transistor circuit is only guaranteed to be able to supply a minimum of about 126mA to the relay coil. If the coil requires more than that, this could the problem. Solution to get more current for the relay coil i...
by ptimlin
Wed Jun 12, 2019 3:12 pm
Forum: Teaching and learning resources
Topic: Learning Basic Electronics
Replies: 7
Views: 1759

Re: Learning Basic Electronics

I will add your local library may already be subscribed to some online learning sites. For example, my local (USA based) library subscribed to Lydia.com where there are a ton of education videos and tutorials including things like electricity/electronics and Python. Go to your libraries web site and...
by ptimlin
Fri May 31, 2019 8:39 pm
Forum: Automation, sensing and robotics
Topic: Detecting 250VAC voltage/current of deep well pump motor
Replies: 45
Views: 15938

Re: Detecting 250VAC voltage/current of deep well pump motor

The wall wart's output is rated for 3v3 at 2 amps. It does seem like a lot of juice to dissipate for what I'm trying to do. One quick and dirty method to dissipate the wall-wart energy is to put a low resistance across the output (tens of ohms). Then to the Pi you feed this through a diode to isola...
by ptimlin
Tue May 28, 2019 9:10 pm
Forum: Automation, sensing and robotics
Topic: Detecting 250VAC voltage/current of deep well pump motor
Replies: 45
Views: 15938

Re: Detecting 250VAC voltage/current of deep well pump motor

I found that I can get to 3v3 with R1: 1700 and R2: 3300. How would I integrate the 10K pulldown resistor to ensure the RPi GPIO doesn't float when the wall wart is not powered? You don't need a 10k pulldown. Output of charger is +5V, one side goes to the GND of your Pi. The other side goes through...
by ptimlin
Tue May 28, 2019 8:56 pm
Forum: Automation, sensing and robotics
Topic: LED Watt / Amp question
Replies: 3
Views: 542

Re: LED Watt / Amp question

Getting about 800-1000 lumens for 10W on LEDs sounds about right, so I am guessing the 10W is the real power being used by the LED light. I assume when you say you hooked up the transformer and the "lights" ran without the transformer getting hot, you were actually talking about ONE light? Not light...
by ptimlin
Tue May 28, 2019 8:47 pm
Forum: Automation, sensing and robotics
Topic: how to control 24VDC valve with ULN2803A?
Replies: 24
Views: 2192

Re: how to control 24VDC valve with ULN2803A?

Just a design note that I think is important to know when working with the ULN2803A and others driver ICs of the same types (ULN2003, etc.) which I don't think was mentioned in this thread the first time around and worth mentioning since the new poster is wanting to drive 8 relays with a single IC. ...
by ptimlin
Mon May 20, 2019 7:08 pm
Forum: Automation, sensing and robotics
Topic: DS18B20: Influence of supply voltage on temperature
Replies: 16
Views: 731

Re: DS18B20: Influence of supply voltage on temperature

that the almost certainly increased 'wasted' current flow with increased supply voltage through the circuitry around the sensor was heating it up, so that it was correctly reading a higher temperature. I still don't think so. These sensors have been around for decades, long before Raspberry Pis exi...
by ptimlin
Sat May 18, 2019 6:18 pm
Forum: Automation, sensing and robotics
Topic: DS18B20: Influence of supply voltage on temperature
Replies: 16
Views: 731

Re: DS18B20: Influence of supply voltage on temperature

But to answer your question, I am not sure why the change in Vdd to the sensor would change the temperature reading. Could it be something as simple as heating due to increased power dissipation in the sensor at the higher supply voltage? Scrubbing the data sheet for the sensor, there is nothing to...
by ptimlin
Wed May 15, 2019 5:37 pm
Forum: Automation, sensing and robotics
Topic: DS18B20: Influence of supply voltage on temperature
Replies: 16
Views: 731

Re: DS18B20: Influence of supply voltage on temperature

To confirm, you are running a three wire system where three separate wires run out to the sensor? And as rpdom asked, the pull up should remain between 3.3V and your GPIO line regardless if you power the sensor from 3.3V or 5V. Also is the pull up resistor next to the Pi or next to the sensor? I bel...
by ptimlin
Sun May 12, 2019 4:40 am
Forum: Beginners
Topic: Small part fell off my pi
Replies: 20
Views: 762

Re: Small part fell off my pi

Most likely it is a small filter capacitor and your Pi will work fine without it.
by ptimlin
Thu May 02, 2019 7:36 pm
Forum: Beginners
Topic: Multiple LEDs - series, parallel, both?
Replies: 6
Views: 298

Re: Multiple LEDs - series, parallel, both?

Just a few random observations that might answer some of your questions (I didn't carefully read everything you wrote so sorry if I am "answering" something you didn't ask. With the very first photo you are using PC817 opto couplers. The first mistake most of us make when we started to use these typ...
by ptimlin
Thu May 02, 2019 6:48 pm
Forum: Other projects
Topic: Automate water heater - Temp sensor/110v relay/switch
Replies: 4
Views: 293

Re: Automate water heater - Temp sensor/110v relay/switch

The Pi's GPIO pins are usually not up to the task of driving most mechanical relays and many solid state relays (SSR). Usually you will need some sort of interface between the two. What is the wattage of the heater you plan to use? I know you said "110V" at somewhere between 8-10 amps, but verifying...
by ptimlin
Thu May 02, 2019 5:25 pm
Forum: Beginners
Topic: Controlling temperature chamber using Peltier and PWM signal with external power source
Replies: 26
Views: 946

Re: Controlling temperature chamber using Peltier and PWM signal with external power source

Would you mind giving me direction on how to select the proper type of Peltier for heating purposes? :) Thank you! Sorry for my many questions! As others have mentioned, if you only need to heat and not cool, then a peltier is an overly complicated way to do it. Just use heating elements instead. T...
by ptimlin
Thu May 02, 2019 4:50 pm
Forum: Automation, sensing and robotics
Topic: Outdoor Pond Water Level Control / Valve
Replies: 9
Views: 561

Re: Outdoor Pond Water Level Control / Valve

While I can appreciate if the idea is to learn to use the Pi for something like this then I say have at it. But if the idea is simply to get an auto top off for the ponds, any reason why you can not use plain old mechanic float switches that simply open or close a water valve? Search for something l...
by ptimlin
Thu May 02, 2019 3:51 pm
Forum: Automation, sensing and robotics
Topic: Sump pump alarm
Replies: 4
Views: 304

Re: Sump pump alarm

I have been thinking about a project along the same lines. A couple of things I have thought about you may also want to consider. One reason a sump will fill too high is because of a power outage and no way to run the sump pump. This would mean without extra battery power for various components (Pi ...
by ptimlin
Sat Apr 06, 2019 6:20 pm
Forum: Automation, sensing and robotics
Topic: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?
Replies: 16
Views: 916

Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

TL;DR past paragraph one. So will only comment on one part of paragraph one. You wrote: "Most of the companies producing end-user electronics are doing so via China - yet the Chinese relays can't be trusted?" We are not talking about components manufactured in China for known brands with good design...
by ptimlin
Sat Apr 06, 2019 6:09 pm
Forum: Automation, sensing and robotics
Topic: How best to control higher voltage relays with 12v/24v coils?
Replies: 26
Views: 1175

Re: How best to control higher voltage relays with 12v/24v coils?

Quick clarification question. You mentioned you would need to have all 16 relays on at the same time. Is this always the case (all on or all off)? Or are their times when you would need to individually control some of them? If it is all on or all off, then you can simplify the entire design by drivi...
by ptimlin
Fri Apr 05, 2019 3:43 pm
Forum: Automation, sensing and robotics
Topic: Wiring relay to Pi
Replies: 27
Views: 1203

Re: Wiring relay to Pi

So the 15-20mA is the current required to switch the actual relay ie current drawn by the coil. this is being switch be the transistor on the relay board, so all we are doing it switching this transistor on using the opto isolator so it should only require a few mA to switch that transistor, but as...
by ptimlin
Fri Apr 05, 2019 3:36 pm
Forum: Automation, sensing and robotics
Topic: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?
Replies: 16
Views: 916

Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

A couple of points. One, relays are much more than simply a coil and some contacts. A lot of R&D goes into developing relays and there is a WIDE range of technologies and materials used in various relays, even if they all just say "DPDT" in the specification. So the better relays are not charging mo...
by ptimlin
Fri Apr 05, 2019 3:24 pm
Forum: Automation, sensing and robotics
Topic: How best to control higher voltage relays with 12v/24v coils?
Replies: 26
Views: 1175

Re: How best to control higher voltage relays with 12v/24v coils?

The ULN2803A could work as well. The thing to keep in mind is that this one is a Darlington configuration so you might lose as much as a voltage on the output so that when you pull the output low it may only get down to 1V or so when pulling a hundred milliamps or more. So keep that in mind of drivi...
by ptimlin
Wed Apr 03, 2019 9:38 pm
Forum: Automation, sensing and robotics
Topic: Wiring relay to Pi
Replies: 27
Views: 1203

Re: Wiring relay to Pi

The problem is not enough current for the relay coil. Optocouplers have what is known as a current transfer ratio. Meaning, the output current available will be some ratio of the input current driving the LED. The 4N26 has a transfer ratio of about 50% (output current available is half of what you d...
by ptimlin
Wed Apr 03, 2019 9:12 pm
Forum: Automation, sensing and robotics
Topic: Garden automation electronics schematic
Replies: 6
Views: 456

Re: Garden automation electronics schematic

Hi again, So a quick look and I don't see anything too concerning. To answer your original questions. 1) yes I would go with the MOSFET over the TIP120 in this application. Even at lower currents the TIP120 (a BJT (bipolar junction transistor) would likely require a heatsink where as the MOSFET is p...
by ptimlin
Wed Apr 03, 2019 7:50 pm
Forum: Automation, sensing and robotics
Topic: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?
Replies: 16
Views: 916

Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Those little relays are nice, but (1) are only single pole (we really need two) and (2) will not cope with the inrush current of the big SMPSs it's going to be switching. They can have an inrush measured in tens of amps. A Dell server I know with a similar power requirement is specified to have not...
by ptimlin
Wed Apr 03, 2019 6:58 pm
Forum: Automation, sensing and robotics
Topic: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?
Replies: 16
Views: 916

Re: Know where I can get reasonably priced DPST/DPDT 240v/8a to 240v/10a relays?

Thanks - that's more or less what I'm finding. My reasonable price would be to stay around $50-$75 for the 16 relays. I mean - when you can get 16 SPDT relays rated for 250V/10A on a PCB with optocouplers, LED indicators, etc... for a total of $15 - $18 per relay seems unreasonable. I mean, It's a ...
by ptimlin
Wed Apr 03, 2019 6:30 pm
Forum: Automation, sensing and robotics
Topic: Garden automation electronics schematic
Replies: 6
Views: 456

Re: Garden automation electronics schematic

Do you have an actual schematic you can share (the photo you posted is a wiring diagram)? Hard to comment when you can not see which components are being used in the design.

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